[instant] Include declaration location of instant config in validation errors by eps1lon · Pull Request #90169 · vercel/next.js

eps1lon · 2026-02-19T00:25:41Z

Adds the declaration location of the instant config to the instant validation errors as a cause.

This works by including a function in each segment with a new SWC transform. The error created in the function is sourcemapped to the right hand side of the export declaration i.e.

export const unstable_instant = ...
                                ^

Most of the time that location is sufficient unless it's a value that's produced somewhere else and just assigned at the export declaration.

A function instead of creating the error during module evaluation has two benefits:

we can create the error lazily when we encounter a validation error
We avoid sourcemapping bugs in the filled app-page template (see [instant] Fix sourcemapping of generated app-page #90200)

nextjs-bot · 2026-02-19T00:48:02Z

Stats from current PR

🔴 1 regression

Metric	Canary	PR	Change	Trend
node_modules Size	473 MB	473 MB	🔴 +89.9 kB (+0%)	█████

📊 All Metrics

📖 Metrics Glossary

Dev Server Metrics:

Listen = TCP port starts accepting connections
First Request = HTTP server returns successful response
Cold = Fresh build (no cache)
Warm = With cached build artifacts

Build Metrics:

Fresh = Clean build (no .next directory)
Cached = With existing .next directory

Change Thresholds:

Time: Changes < 50ms AND < 10%, OR < 2% are insignificant
Size: Changes < 1KB AND < 1% are insignificant
All other changes are flagged to catch regressions

⚡ Dev Server

Metric	Canary	PR	Change	Trend
Cold (Listen)	455ms	455ms	✓	█▁█▁▁
Cold (Ready in log)	434ms	435ms	✓	█▁█▁▁
Cold (First Request)	1.217s	1.261s	✓	█▃█▃▃
Warm (Listen)	456ms	456ms	✓	█▁█▁▁
Warm (Ready in log)	438ms	441ms	✓	█▁█▁▁
Warm (First Request)	341ms	339ms	✓	█▁█▁▁

📦 Dev Server (Webpack) (Legacy)

📦 Dev Server (Webpack)

Metric	Canary	PR	Change	Trend
Cold (Listen)	455ms	455ms	✓	▅▅▁▁▁
Cold (Ready in log)	436ms	436ms	✓	▄▅▄▂▂
Cold (First Request)	1.949s	1.917s	✓	▄▅▁▁▁
Warm (Listen)	455ms	456ms	✓	▄▅▁▁▁
Warm (Ready in log)	435ms	435ms	✓	▅▆▂▃▂
Warm (First Request)	1.922s	1.934s	✓	▄▅▁▂▁

⚡ Production Builds

Metric	Canary	PR	Change	Trend
Fresh Build	4.067s	4.013s	✓	█▁█▁▁
Cached Build	4.114s	4.116s	✓	█▁█▁▁

📦 Production Builds (Webpack) (Legacy)

📦 Production Builds (Webpack)

Metric	Canary	PR	Change	Trend
Fresh Build	13.887s	13.918s	✓	▄▅▁▁▁
Cached Build	14.031s	14.004s	✓	▄▅▁▁▁
node_modules Size	473 MB	473 MB	🔴 +89.9 kB (+0%)	█████

📦 Bundle Sizes

Bundle Sizes

⚡ Turbopack

Client

Main Bundles: **399 kB** → **399 kB** ⚠️ +130 B

80 files with content-based hashes (individual files not comparable between builds)

Server

Middleware

	Canary	PR	Change
middleware-b..fest.js gzip	764 B	769 B	✓
Total	764 B	769 B	⚠️ +5 B

Build Details

Build Manifests

	Canary	PR	Change
_buildManifest.js gzip	451 B	450 B	✓
Total	451 B	450 B	✅ -1 B

📦 Webpack

Client

Main Bundles

	Canary	PR	Change
5528-HASH.js gzip	5.47 kB	N/A	-
6280-HASH.js gzip	57.5 kB	N/A	-
6335.HASH.js gzip	169 B	N/A	-
912-HASH.js gzip	4.53 kB	N/A	-
e8aec2e4-HASH.js gzip	62.6 kB	N/A	-
framework-HASH.js gzip	59.7 kB	59.7 kB	✓
main-app-HASH.js gzip	255 B	254 B	✓
main-HASH.js gzip	39.1 kB	39.1 kB	✓
webpack-HASH.js gzip	1.68 kB	1.68 kB	✓
262-HASH.js gzip	N/A	4.53 kB	-
2889.HASH.js gzip	N/A	169 B	-
5602-HASH.js gzip	N/A	5.48 kB	-
6948ada0-HASH.js gzip	N/A	62.6 kB	-
9544-HASH.js gzip	N/A	58.3 kB	-
Total	231 kB	232 kB	⚠️ +728 B

Polyfills

	Canary	PR	Change
polyfills-HASH.js gzip	39.4 kB	39.4 kB	✓
Total	39.4 kB	39.4 kB	✓

Pages

	Canary	PR	Change
_app-HASH.js gzip	194 B	194 B	✓
_error-HASH.js gzip	183 B	180 B	🟢 3 B (-2%)
css-HASH.js gzip	331 B	330 B	✓
dynamic-HASH.js gzip	1.81 kB	1.81 kB	✓
edge-ssr-HASH.js gzip	256 B	256 B	✓
head-HASH.js gzip	351 B	352 B	✓
hooks-HASH.js gzip	384 B	383 B	✓
image-HASH.js gzip	580 B	581 B	✓
index-HASH.js gzip	260 B	260 B	✓
link-HASH.js gzip	2.5 kB	2.5 kB	✓
routerDirect..HASH.js gzip	320 B	319 B	✓
script-HASH.js gzip	386 B	386 B	✓
withRouter-HASH.js gzip	315 B	315 B	✓
1afbb74e6ecf..834.css gzip	106 B	106 B	✓
Total	7.97 kB	7.97 kB	✅ -2 B

Server

Edge SSR

	Canary	PR	Change
edge-ssr.js gzip	125 kB	125 kB	✓
page.js gzip	252 kB	252 kB	✓
Total	377 kB	377 kB	✅ -101 B

Middleware

	Canary	PR	Change
middleware-b..fest.js gzip	617 B	615 B	✓
middleware-r..fest.js gzip	156 B	155 B	✓
middleware.js gzip	43.8 kB	43.9 kB	✓
edge-runtime..pack.js gzip	842 B	842 B	✓
Total	45.4 kB	45.5 kB	⚠️ +76 B

Build Details

Build Manifests

	Canary	PR	Change
_buildManifest.js gzip	715 B	718 B	✓
Total	715 B	718 B	⚠️ +3 B

Build Cache

	Canary	PR	Change
0.pack gzip	3.92 MB	3.94 MB	🔴 +18.7 kB (+0%)
index.pack gzip	103 kB	102 kB	✓
index.pack.old gzip	103 kB	104 kB	✓
Total	4.12 MB	4.14 MB	⚠️ +18.5 kB

🔄 Shared (bundler-independent)

Runtimes

	Canary	PR	Change
app-page-exp...dev.js gzip	317 kB	318 kB	✓
app-page-exp..prod.js gzip	169 kB	169 kB	✓
app-page-tur...dev.js gzip	317 kB	317 kB	✓
app-page-tur..prod.js gzip	169 kB	169 kB	✓
app-page-tur...dev.js gzip	314 kB	314 kB	✓
app-page-tur..prod.js gzip	167 kB	167 kB	✓
app-page.run...dev.js gzip	314 kB	314 kB	✓
app-page.run..prod.js gzip	167 kB	167 kB	✓
app-route-ex...dev.js gzip	70.6 kB	70.6 kB	✓
app-route-ex..prod.js gzip	49.1 kB	49.1 kB	✓
app-route-tu...dev.js gzip	70.7 kB	70.7 kB	✓
app-route-tu..prod.js gzip	49.1 kB	49.1 kB	✓
app-route-tu...dev.js gzip	70.2 kB	70.2 kB	✓
app-route-tu..prod.js gzip	48.9 kB	48.9 kB	✓
app-route.ru...dev.js gzip	70.2 kB	70.2 kB	✓
app-route.ru..prod.js gzip	48.9 kB	48.9 kB	✓
dist_client_...dev.js gzip	324 B	324 B	✓
dist_client_...dev.js gzip	326 B	326 B	✓
dist_client_...dev.js gzip	318 B	318 B	✓
dist_client_...dev.js gzip	317 B	317 B	✓
pages-api-tu...dev.js gzip	43.2 kB	43.2 kB	✓
pages-api-tu..prod.js gzip	32.9 kB	32.9 kB	✓
pages-api.ru...dev.js gzip	43.2 kB	43.2 kB	✓
pages-api.ru..prod.js gzip	32.8 kB	32.8 kB	✓
pages-turbo....dev.js gzip	52.5 kB	52.5 kB	✓
pages-turbo...prod.js gzip	38.4 kB	38.4 kB	✓
pages.runtim...dev.js gzip	52.5 kB	52.5 kB	✓
pages.runtim..prod.js gzip	38.4 kB	38.4 kB	✓
server.runti..prod.js gzip	63.6 kB	63.6 kB	✓
Total	2.81 MB	2.81 MB	⚠️ +804 B

📝 Changed Files (10 files)

Files with changes:

app-page-exp..ntime.dev.js
app-page-exp..time.prod.js
app-page-tur..ntime.dev.js
app-page-tur..time.prod.js
app-page-tur..ntime.dev.js
app-page-tur..time.prod.js
app-page.runtime.dev.js
app-page.runtime.prod.js
pages-api.runtime.dev.js
pages.runtime.dev.js

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nextjs-bot · 2026-02-19T00:48:16Z

Tests Passed

codspeed-hq · 2026-02-19T01:09:49Z

Merging this PR will not alter performance

✅ 17 untouched benchmarks
⏩ 3 skipped benchmarks¹

_{Comparing sebbie/02-18-_instant_include_declaration_location_of_instant_config_in_validation_errors (0b85dcb) with canary (cd27e54)}

3 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

eps1lon · 2026-02-20T02:59:03Z

test/e2e/app-dir/instant-validation/instant-validation.test.ts

+           |                                 ^",
+             "stack": [
+               "unstable_instant app/suspense-in-root/static/missing-suspense-around-dynamic/page.tsx (3:33)",
+               "Set.forEach <anonymous>",


These are from not filtering anonymous sandwich frames which we'll do eventually.

…ion errors

nextjs-bot added created-by: Next.js team PRs by the Next.js team. Turbopack Related to Turbopack with Next.js. type: next labels Feb 19, 2026

eps1lon force-pushed the sebbie/02-18-_instant_include_declaration_location_of_instant_config_in_validation_errors branch from 9bd49a0 to 6aec01e Compare February 19, 2026 04:50

eps1lon mentioned this pull request Feb 19, 2026

[instant] Fix sourcemapping of generated app-page #90200

Closed

eps1lon force-pushed the sebbie/02-18-_instant_include_declaration_location_of_instant_config_in_validation_errors branch from 5d4106c to 0b85dcb Compare February 20, 2026 02:47

nextjs-bot added the tests label Feb 20, 2026

eps1lon commented Feb 20, 2026

View reviewed changes

eps1lon force-pushed the sebbie/02-18-_instant_include_declaration_location_of_instant_config_in_validation_errors branch from 0b85dcb to d0c6ab9 Compare February 20, 2026 03:59

eps1lon added 9 commits February 19, 2026 20:00

[instant] Include declaration location of instant config in validat…

e454e37

…ion errors

Pass debug instant stack to instant validation cause

e3a85ea

Sourcemap to right hand side

9c86921

Gate behind dev server or debug prerender

186232d

construct with cause instead of mutate

4809f0a

Doctor a nicer looking stack

98fc976

Error message cosmetics

1930849

Create the stack lazily instead of in an iife

c001d9c

Create errors lazily so that we can mutate their messages

ce47c91

eps1lon force-pushed the sebbie/02-18-_instant_include_declaration_location_of_instant_config_in_validation_errors branch from d0c6ab9 to ce47c91 Compare February 20, 2026 04:00

eps1lon requested review from lubieowoce and unstubbable February 20, 2026 04:02

eps1lon marked this pull request as ready for review February 20, 2026 04:02

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[instant] Include declaration location of instant config in validation errors#90169

[instant] Include declaration location of instant config in validation errors#90169
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sebbie/02-18-_instant_include_declaration_location_of_instant_config_in_validation_errors

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